The present invention relates to an ultraviolet and vacuum ultraviolet antireflection substrate. In particular, it relates to an antireflection substrate suitable for various low-reflection lenses, substrates of low-reflection photomasks and substrates of low-reflection pellicles (pellicle membranes) used in exposure to light in the ultraviolet and vacuum ultraviolet regions in manufacture of semiconductor integrated circuits.
In recent years, the resolution of exposure systems for fabrication of semiconductor integrated circuits is increasing in order to improve the integration of semiconductor circuits. Exposure light having shorter wavelengths is increasingly used to improve the resolution of exposure systems, and exposure light has changed from g-line (wavelength: 435 nm) to i-line (wavelength: 365 nm) and then to KrF excimer laser beams (wavelength: 248 nm) in current use. Even ArF excimer laser beams (wavelength: 193 nm) and F2 laser beams (wavelength: 157 nm) in the vacuum ultraviolet region are being put into practical use.
These exposure systems use optical materials such as lenses, photomasks and pellicles, which serve as dust covers for photomasks. A familiar material for lenses and photomasks is synthetic quartz glass, while synthetic quartz glass and transparent fluoroplastics are known as materials for pellicle membranes.
However, the refractive indices of such materials as synthetic quartz glass and transparent fluoroplastics increase as the wavelength of the exposure light becomes shorter, and therefore, if nothing is done, the light loss resulting from surface reflection and the development of flare ghosts are prominent. There is another problem that the high light transmission, for example, of at least 95%, required in the ultraviolet region and the vacuum ultraviolet region is not secured.
Therefore, the first object of the present invention is to provide an antireflection substrate which suppresses light loss resulting from surface reflection and development of flare ghosts in the ultraviolet region and the vacuum ultraviolet region.
The second object of the present invention is to provide an antireflection substrate having high light transmission.
The present invention provides an ultraviolet and vacuum ultraviolet antireflection substrate (hereinafter referred to as xe2x80x9cthe first substratexe2x80x9d) comprising a substrate which is transparent to ultraviolet and vacuum ultraviolet rays in the wavelength region from 155 nm to 200 nm and a monolayer antireflection film formed on at least one side of the substrate, wherein the center wavelength xcex0 of the wavelength region of ultraviolet or vacuum ultraviolet light which needs antireflection, the refractive index ns of the substrate at the wavelength of xcex0, the refractive index n1 of the antireflection film at the wavelength of xcex0 and the physical thickness d1 of the antireflection film satisfy the conditions that n1 less than ns, and that n1d1 is almost (1/4+m/2)xcex0 (wherein m is an integer of at least 0).
In the present invention, n1d1 being almost (1/4+m/2)xcex0 (m is an integer of at least 0) means that (0.187+m/2)xcex0xe2x89xa6n1d1xe2x89xa6(0.327+m/2)xcex0.
The present invention also provides an ultraviolet and vacuum ultraviolet antireflection substrate (hereinafter referred to as xe2x80x9cthe second substratexe2x80x9d) comprising a substrate which is transparent to ultraviolet and vacuum ultraviolet rays in the wavelength region from 155 nm to 200 nm and a bilayer antireflection film comprising a second layer and a first layer formed on at least one side of the substrate in this order from the substrate side, wherein the center wavelength xcex0 of the wavelength region of ultraviolet or vacuum ultraviolet light which needs antireflection, the refractive index ns of the substrate at the wavelength of xcex0, the refractive index n2 of the second layer at the wavelength of xcex0, the physical thickness d2 of the second layer, the refractive index n1 of the first layer at the wavelength of xcex0, and the physical thickness d1 of the first layer satisfy the conditions that n1 less than ns less than n2, that n1d1 is almost (1/4+m/2)xcex0 (wherein m is an integer of at least 0), and that 0.05xcex0xe2x89xa6n2d2xe2x89xa60.50xcex0.
The present invention further provides an ultraviolet and vacuum ultraviolet antireflection substrate (hereinafter referred to as xe2x80x9cthe third substratexe2x80x9d) comprising a substrate which is transparent to ultraviolet and vacuum ultraviolet rays in the wavelength region from 155 nm to 200 nm and a trilayer antireflection film comprising a third layer, a second layer and a first layer formed on at least one side of the substrate in this order from the substrate side, wherein the center wavelength xcex0 of the wavelength region of ultraviolet or vacuum ultraviolet light which needs antireflection, the refractive index ns of the substrate at the wavelength of xcex0, the refractive index n3 of the third layer at the wavelength of xcex0, the physical thickness d3 of the third layer, the refractive index n2 of the second layer at the wavelength of xcex0, the physical thickness d2 of the second layer, the refractive index n1 of the first layer at the wavelength of xcex0, and the physical thickness d1 of the first layer satisfy the following conditions (1) to (4):
n1, n3 less than ns and n1, n3 less than n2,xe2x80x83xe2x80x83(1) 
xe2x80x830 less than n1d1xe2x89xa60.47xcex0,xe2x80x83xe2x80x83(2)
0.14xcex0xe2x89xa6n3d3xe2x89xa60.33xcex0,xe2x80x83xe2x80x83(3) 
and
0.16xcex0xe2x89xa6n2d2xe2x89xa60.38xcex0,xe2x80x83xe2x80x83(4) 
0.64xcex0xe2x89xa6n2d2xe2x89xa60.86xcex0, 
or
1.13xcex0xe2x89xa6n2d2xe2x89xa61.35xcex0.